The Sandbox as Megadungeon

While fretting about the lack of a Planet Algol campaign megadungeon and reflecting on the carnage of the previous session, I was struck by the realization that in the case of my campaign the sandbox is the megadungeon. I have certainly read theory regarding that subject in the past, but now it was real...

My intention wasn't to make a hexmap, outdoor megadungeon, but instead to ape previous efforts such as the original Wilderlands, Carcosa, and so forth in order to create a sandbox to run an old school D&D game in. However, once the mechanics of wilderness adventuring (especially the rules for getting lost) started coming into play and the players got in the swing of the sandbox, it started feeling, for me, very dungeony.

It's interesting to note that the map for a text-based adventure game or MUDD would look the same regardless of whether it was of a dungeon or an outdoor area. That's what's happening with me. Dungeon, Wilderness, they're just labels. They both contain monsters, treasures, traps, tricks, potential allies, M.A.R. Barker-esque "Saturday Night Specials," parties of adventurers can get lost and die in both of them, etc.

"But...the Megadungeon is the Mythic Underworld!" You exclaim, "that's what differentiates it from wilderness and lairs!"

My campaign was designed from the very start to function as an outdoor analogue of the Mythic Underworld. The planet, the solar system, history, the races, are designed to be weird, irrational, unpredictable, dangerous. To quote from Philotomy's OD&D Musings:

"Some common characteristics and philosophies for a mythic underworld dungeon (keep these in mind when creating your dungeon):

• It's big, and has many levels; in fact, it may be endless
• It follows its own ecological and physical rules
• It is not static; the inhabitants and even the layout may grow or change over time
• It is not linear; there are many possible paths and interconnections
• There are many ways to move up and down through the levels
• Its purpose is mysterious or shrouded in legend
• It's inimical to those exploring it
• Deeper or farther levels are more dangerous
• It's a (the?) central feature of the campaign"
  

I believe that the above points would also apply to a good fantasy campaign world as well...